This invention relates to an apparatus and a method for processing images and a system and a method for transmitting and receiving images as well as a providing medium that are particularly adapted to carry out color signal processing operations that may vary as a function of individual image display apparatus in order to coordinate the colors of images to be displayed there so as to eliminate apparatus-dependency of the colors of images.
As a result of the rapid spread of DTP (desk top publishing) and the Internet in recent years, color images are manipulated more often than ever on the display screens of CRT (cathode ray tube) displays and liquid crystal displays.
For example, operations of drawing pictures by means of painting tools are being replaced by those of drawing computer graphics by means of personal computers. Consumers place orders by seeing images of products displayed on the display screen as electronic advertisements that are transmitted by way of the Internet.
In any of such cases, it is necessary that the colors of the original picture (which may be a picture drawn by an artist or a photographic picture) and those of the facsimile image of the picture output by an apparatus (which may be the monitor screen of a display apparatus or a color printer) agree with each other.
Thus, it is highly desirable that, for a same picture, the image displayed on the display screen of a personal computer and the image output by a printer appear same in terms of their colors.
In the case of an electronic advertisement, if the image of an article (e.g., a jacket or a painting) displayed on the display screen of the personal computer of a consumer appears differently from the actual commodity, a trouble may arise between the commodity provider and the consumer when the consumer buys the commodity.
Thus, it is necessary to provide an arrangement in which a picture appears exactly the same on all the image display apparatus displaying an image of the picture particularly in terms of colors.
A system referred to as CMS (color management system) is known for correcting the differences of colors of images of the same picture among different image display apparatus displaying it.
FIG. 1 of the accompanying drawings schematically illustrate a CMS. Referring to FIG. 1, with a CMS, the color signals of a picture input through an input device (e.g., camera 1, scanner 2, monitor 3) are converted into common color space signals (e.g., CIE/XYZ, CIE/L*a*b*) that are not dependent on the characteristics of the device and then output through an output device (e.g., monitor 3, printer 4).
A conversion formula or a conversion table that is referred to as xe2x80x9cprofilexe2x80x9d and specific to each device is used when converting a signal into that of a common color space. For examples, the color signals of a picture taken by camera 1 are converted into common color space signals by the profile specific to the camera 1. To output the signals through monitor 3, the common color space signals are then converted into color signals that reflect the characteristics of the monitor 3 by the profile specific to the monitor 3 and an image of the picture formed by the obtained color signals will be displayed on the monitor.
Such a profile is determined by means of the signal values input to the device and the color values (XYZ values or L*a*b* values) obtained by observing the colors of the image output according to the signal values typically through a calorimeter.
FIG. 2 of the accompanying drawings a chart showing the flow of data when the image on the monitor 3 is output to printer 4. Referring to FIG. 2, the image on the monitor 10 is converted into signals of a common color space by the profile specific to the monitor 3 (monitor profile 20). In other words, the image data (RGB data) of the monitor 3 are converted respectively into corresponding quantities of light by means of TRCs (tone reproduction curve, which will be described hereinafter) generated by TRC generator section 20-1. The quantities of light for RGB reflect the colors of the image viewed by the user on the monitor 3.
The data (on the quantities of light for RGB) generated by the TRC generator section 20-1 are then processed for conversion using a matrix representing the linear relationship between the quantities of light output to the monitor 3 and the CIE/XYZ values (or L*a*b* values) to obtain a series of values (CIE/XYZ values or L*a*b* values), which are then output as common color space signals 30.
The common color space signals 30 obtained by the monitor profile are then processed for conversion by the profile specific to the printer 4 (printer profile 40) to reflect the printing characteristics of the printer 4 and the obtained color signals for the printer, or CMY50, are printed and output.
Apparatus of a same type can show disparity, if slightly, in the characteristics depending on individual apparatus. Then, the profile is preferably calibrated for each apparatus.
The profiles of the monitors marketed by a same manufacturer can be calibrated typically by means of a monitor calibration tool or characterization tool provided by the manufacturer.
The monitor profile 20 is prepared by such a tool. FIG. 3 of the accompanying drawings is a flow chart of the operation of preparing a monitor profile. Referring to FIG. 3, firstly in Step S1, TRCs (g-curves) representing the non-linear relationship between the RGB data to be input to the monitor and the quantities of light of RBG of the monitor is prepared. Such TRCs can be obtained by observing the XYZ3-stimulus values of more than ten tones (e.g., 16 tones) sampled at regular intervals from the full range of tones (e.g., 256 tones) for each of the primary colors of red (R), green (G) and blue (B) of the RGB data (or RGBW data) and applying them to the g equation out of equations (1) shown below by non-linear regression (a TRC is obtained by linear interpolation or a conversion table if the number of samples is large).                                                         r              =                                                                    X                    r                                                        X                                          r                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                            =                                                      {                                                                                            K                                                      r                            ,                            gain                                                                          ⁡                                                  (                                                      dr                                                                                          2                                N                                                            -                              1                                                                                )                                                                    +                                              K                                                  r                          ,                          offset                                                                                      }                                                        γ                    r                                                                                                                          g              =                                                                    Y                    g                                                        Y                                          g                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                            =                                                      {                                                                                            K                                                      g                            ,                            gain                                                                          ⁡                                                  (                                                                                    d                              ⁢                                                              xe2x80x83                                                            ⁢                              g                                                                                                                      2                                N                                                            -                              1                                                                                )                                                                    +                                              K                                                  g                          ,                          offset                                                                                      }                                                        γ                    g                                                                                                                          b              =                                                                    Z                    b                                                        Z                                          b                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                            =                                                      {                                                                                            K                                                      b                            ,                            gain                                                                          ⁡                                                  (                                                      db                                                                                          2                                N                                                            -                              1                                                                                )                                                                    +                                              K                                                  b                          ,                          offset                                                                                      }                                                        γ                    b                                                                                                          (        1        )            
In the above equations (1), variables dr, dg and db respectively represent the input signal values for red, green and blue and variable N represent the number of bits of each input signal. Coefficient kgain represents the gain of each of the colors (e.g., kr.gain represents the gain of red) and coefficient koffset represent the offset of each of the colors (e.g., kr.offset represents the offset of red). Additionally, variables Xr, Yg and Zb respectively represent the 3-stimulus values of the three colors and variable Xr.max, Yg.max and Zb.max respectively represent the 3-stimulus values of the three colors when the input signal values are maximal. Thus, variables r, g and b are obtained by normalizing Xr, Yg and Zb respectively by the maximum values Xr.max, Yg.max and Zb.max to take a value between 0 and 1.
FIG. 4 is a flow chart illustrating the operation of preparing a TRC corresponding to an input digital signal for red in Step S1 of FIG. 3. Referring to FIG. 4, in Step S21, XYZr values (including maximum value XYZr.max) are observed for the sampled several tones from the input signal corresponding to red. Then, in Step S22, the input signal values dr are normalized by dividing them by 2Nxe2x88x921 and, in Step S23, the output brightness values are normalized by dividing Xr values by the maximum value Xr.max. In Step S24, a process of non-linear interpolation is conducted by means of equations (1). Finally, in Step S25, the values of coefficients kr.offset, kr.gain and xcex3r are determined. Note that operations of preparing TRCs corresponding to input digital signals dg and db for green and blue will be conducted similarly.
FIGS. 5A through 5C are exemplary TRCs for red, green and blue prepared in a manner as described above.
Generally, xcex3 values for a monitor refers to those of xcex3s in equations (1). Note that most of the currently available tools utilizes kgain=1.0 and koffset=0 in equations (1).
Returning to FIG. 3, in Step S2, a matrix representing the linear relationship between the quantities of light of RGB and the monitor and the CIE/XYZ values are determined. If, for example, the monitor in question is of the self-emission type and the law of addition approximately holds true for the quantities of light (r, g, b) when mixing colors, then the CIE/XYZ3-stimulus values (XCRT, YCRT, ZCRT) can be obtained from the quantities of light of RGB corrected in Step S1 (normalized values) and a 3xc3x97m matrix as described below. For the purpose of simplification, a matrix of 3xc3x973 which is of the most simple form, is shown below.                               [                                                                      X                  CRT                                                                                                      Y                  CRT                                                                                                      Z                  CRT                                                              ]                =                              [                                                                                X                                          r                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  X                                          g                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  X                                          b                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                                              Y                                          r                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  Y                                          g                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  Y                                          b                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                                              Z                                          r                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  Z                                          g                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                                  Z                                          b                      ,                                              m                        ⁢                                                  xe2x80x83                                                ⁢                        a                        ⁢                                                  xe2x80x83                                                ⁢                        x                                                                                                                  ]                    ⁡                      [                                                            r                                                                              g                                                                              b                                                      ]                                              (        2        )            
Such a matrix can be obtained by observing the XYZ3-stimulus values of each of the three primary colors for the highest brightness.
Note that, in most of the known tools of the type under consideration, the TRCs and the matrix are determined on an assumption that the monitor is not affected by ambient light and used in the dark and the monitor profile is obtained and the TRCs are corrected on the basis of them.
Thus, as shown in FIG. 6, when ambient light is present, the values (CIE/XYZ values) obtained from the image on the monitor will be those of the colors of the self-emission type monitor (XCRT, YCRT, ZCRT) plus those of the colors of ambient light reflected by the surface of the tube of the monitor (Rbkxc3x97(XAmb, YAmb, ZAmb)) because ambient light is reflected by the surface of the tube of the monitor so that consequently they may be different from those observed when the profile was prepared (in the dark). Thus, there is a problem accompanying such known tools that the colors of the images on the monitor cannot be accurately corrected when ambient light exists.
Additionally, as seen from FIG. 7A, the TRC brightness will increase (shift from curve a to curve b) when ambient light is present. In FIG. 7A, the horizontal axis represents the value of the normalized input digital signal (or the value of the input digital signal divided by the value of the maximum input digital signal of the monitor) and the vertical axis represent the output brightness of the monitor.
FIG. 7B is a graph obtained by normalizing the vertical axis of FIG. 7A by the value of the maximum brightness. As seen from FIG. 7B, the monitor shows a narrower dynamic range (D2 less than D1) when ambient light is present (and its performance reflects curve bxe2x80x2 with a dynamic range of D2) than when ambient light is not found (and its performance reflects curve axe2x80x2 with a dynamic range of D1).
Thus, the dynamic range is narrowed when ambient light exists so that consequently the image on the monitor lacks sharp contrast to the viewer because of the partly lost dynamic range.
Now, the monitor is provided with a function that allows the user to arbitrarily regulate the contrast, the brightness and the reference white (neutral) point of the monitor. If the function is used to change the contrast, the brightness and the reference white point, the TRC characteristics measured when the profile is prepared (the relationship between the values of the input digital signals and the quantities of light of RGB output to the monitor) will also have to be changed. If such is the case, the characteristics of the monitor will have to be measured once again to update the TRCs in order to accurately correct the colors. However, it is practically impossible to measure the characteristics of the monitor each time the above function is used and hence there exits a problem of a difficulty with which the colors are accurately corrected on the monitor.
Thus, it is necessary to maintain the conditions under which the profile is prepared (that the monitor is used in the dark and the contrast, the brightness and the reference white point at the time of shipment are kept unchanged) in order to accurately correct the colors on the monitor. If this requirement is not met and the conditions have been altered, the characteristics of the monitor have to be measured once again under the current conditions.
It is a first object of the present invention to provide an apparatus and a method for processing images as well as a providing medium that are adapted to properly correct the colors of images.
According to a first aspect of the invention, the chromatic profile of a monitor to be used for outputting an image is adapted to update the profile depending on the information obtained on the viewing environment. Thus, if ambient light changes, the monitor profile will be automatically updated to realize color matching without measuring the operating characteristics of the monitor once again.
It is a second object of the present invention to provide an apparatus and a method for processing images as well as a providing medium that are adapted to automatically update the chromatic profile of a monitor for color matching.
According to a second aspect of the invention, information on the setting of a monitor to be used for outputting an image is obtained and input and the chromatic profile of the monitor is updated according to the obtained input information so that the updated profile is stored in the monitor. Thus, if the user arbitrarily change the setting of the monitor, the operating characteristics of the monitor do not have to be measured after the change because the monitor profile is automatically updated for color matching.
It is a third object of the invention to provide a system and a method for transmitting/receiving images as well as a providing medium that are adapted to make the appearance of the image at the transmitter agree with that of the image at the receiver in terms of colors.
According to a third aspect of the invention, the chromatic profile of the input device, information on the initial operating conditions of the input device when the profile is prepared and information on the current operating conditions of the input device are added in the transmitter to the image data to be transmitted and sent to the receiver which, upon receiving the transmitted image data, extracts the profile, the information on the initial operating conditions and the information on the current operating conditions from the received image data and performs a processing operation of correcting the colors for the image data. Thus, when an image input through the input device of the transmitter is output to the output device of the receiver by way of the internet, for example, and the transmitted cannot update the profile in response to ambient light and the information on the setting of the input device, the output device of the receiver can perform the updating operation for the transmitter in order to make the appearance of the image at the transmitter agree with that of the image at the receiver in terms of colors.
It is a fourth object of the invention to provide an apparatus and a method for processing images as well as a providing medium that are adapted to accurately calibrate the chromatic profile of a monitor with a minimal amount of data obtained by measurement if the black level is isolated.
According to a fourth aspect of the invention, a 3xc3x974 matrix containing elements for offsetting the light emitting components of the display section in a state where the image data is equal to 0 will be generated to obtain color signals that are not dependent on the device in response to the outcome of detecting the emission of light of the display section in a state where the image data is equal to 0 and that of detecting if the law of addition holds true for mixed colors. Thus, the chromatic profile of the monitor can be accurately calibrated with a minimal amount of data obtained by measurement if the black level is isolated.
It is a fifth object of the invention to provide an apparatus and a method for processing images as well as a providing medium that are adapted to accurately carry out an operation of chromatic calibration with a minimal amount of data obtained by measurement.
According to a fifth aspect of the invention, a total of nine tone reproduction curves will be generated in response to the outcome of detecting if the law of proportion holds true or not and then formulas will be generated to obtain color signals that are not device-dependent from the nine tone reproduction curves and the 3-stimulus values for the black level. Thus, the chromatic profile of the monitor can be accurately with a minimal amount of data obtained by measurement.